(Supported by NIH A134354-05 to R. Limberger) Treponema denticola is a motile, fastidious bacterium that is often found associated with severe periodontal lesions. The motility of treponemes is responsible in part for their pathogenesis, and T. denticola is an excellent model for studying motility. We wish to determine the function and regulation of treponemal polypeptides that are strongly associated with motility. One important polypeptide to be analyzed is CfpA, which comprises the unique cytoplasmic filaments of treponemes, which have an unknown function. We hypothesize that the cytoplasmic filaments have a role in motility, either directly through association with the periplasmic flagellum or indirectly through maintenance of cell shape. This hypothesis will be tested by analysis of cfpA-interrupted mutants of T. denticola together, with a detailed structural analysis of the cytoplasmic filaments using high-voltage electron microscopy and image analysis. This aim is important for support of our motility studies because the close structural relationship between the cytoplasmic filaments and the periplasmic flagellum has not been adequately studied. The objectives of this research are to understand treponemal motility by analysis of relevant genes and cell structures that are involved in cell movement. These analyses will also have broad applications to many spirochetes and include pathogenesis, gene regulation, cell movement and intracellular communication. A single-tilt IVEM tomographic reconstruction was made from a 0.25(m plastic section. We are unable to clearly identify the cytoplasmic filaments in the reconstruction. It was later discovered that we were not given the strain Treponema denticola but Treponema phagadenis. Subsequently, 0.5(m sections from Dr. Goldstein's 1996 research with Treponema denticola were examined using the HVEM in hopes of seeing cytoplasmic filaments. None were clearly seen.